XV SOUTH AMERICAN RODENTS 487 absent,1 an exceptional state of affairs in Rodents. A singular fact in the anatomy of this animal is the existence of a septum dividing the lower part of the trachea. This is sometimes met with in birds. As might be supposed from its large eyes, the Spring Haas, as the animal is sometimes called, is nocturnal. Its long hind-limbs permit it to leap enormous distances. It is a burrowing Rodent. SECTION 3. HYSTRICOMORPHA. Fam. 1. Octodontidae.—The Rodents of this family are of small to moderate size, the only, relatively speaking, giant in the family being the "'Water-Rat/' Myoca&tor. The toes are with but one exception not reduced ; the tail is long in the majority of the genera. The teats are placed high up on the sides of the body. The clavicle is fully ossified. All the genera are South or Central American in range with the exception of Petromys? Sub-Fam. 1. Octodontinae.—Octodon has four species, which are all Chilian, Peruvian, and Bolivian in distribution. The Degu, O. degust has a length of 160 mm., with a tail 105 mm. long. The ears are 18 mm. long. At the roots of the claws are longish and stiff hairs which appear to serve as " combs." The tail has long but sparsely scattered hairs. There are twelve pairs of ribs. The lengths of the various sections of the intestine are as follows: small intestine, 680 mm.; caecum, 90 mm.; large intestine, 390 mm. These animals live in large companies. Closely allied is the genus HaJbrocoma (more correctly, as it appears, to be written ^4.1brocoma), with two species. M. bennetti is 204 mm. long, with a tail of 103 mm. The ears are long, 22 mm. The fore-feet have no outward trace of the thumb. Stiff hairs like those that characterise Octodon are found also in this genus. The fur is very soft. The furring of the tail is much thicker than in Octodon. Spalacopus with but a single species,, S. poeppigi, is a burrow- ing animal, from 'which indeed, and on account of its resemblance to Spalax, it has received its name. The ears in accordance with the underground life are short, only 5 mm. in length in an 1 Parsons, Proc. Zool. Soc. 1898, p. 858. 3 Very probably this form should be rather, as it is by Thomas, referred to the neighbourhood of Pectinator, which would clear up the geographical anomaly.